Circeis spirillum (Linnaeus, 1758)

Common name(s):

Circeis spirillum, top individual's
tube coil is 1 mm in diameter, living on an Abietinaria
constans hydroid. Note the dark operculum
held near the center of the coil on the top individual.

(Photo by: Dave Cowles, August 2014)

Description: Members of Family
Spirorbidae has most or all segments not longer than wide.
The head has a series of radioles
and an operculum.
Members of the family are quite small and build a distinctive coiled, calcareous
tube attached to the substrate (the part that attaches to the substrate
is the dorsal side).
The thoracic region of
the worm's body has only 4 setigers. Circeis
spirillum builds a thin, translucent calcareous tube that is round
in cross section and always spirals dextrally
(counterclockwise). The end of the tube usually points upward from
the substrate (but not in this individual). The collar setae are
obliquely geniculate,
and have cross striations. The embryos are attached singly to the
inside of the tube.

How to Distinguish from Similar Species:Circeis
armoricana has collar setae that are sharply geniculate
and have no cross striations, the tube is porcellanous rather than clear,
and it lives on shells, kelp, or decapods. Several Spirorbis
species have tubes that coil sinestrally
(clockwise).

Geographical Range: Circumboreal
(Arctic, North Pacific, and North Atlantic), but no farther south than
where the water reaches 15 degrees C in August.